Adult Birthday Party Invitation Etiquette

Hello! I am having a surprise 40th birthday party for my husband. It is at a restaturant, and there will be wine and appetizers served while the guests are waiting for us to arrive, but they will be expected to pay for their own dinner. Should I include something on the invitation, or will people just assume because it is at a restaurant they will have to pay?? HELP!!
Posted by Heather; updated 01/09/10